The present invention relates to a cassette for a printing ribbon for typewriters comprising a casing, a supply spool which is accommodated in the casing and has a tube on to which the printing ribbon is wound, and an anti-unrolling element to prevent unrolling movements of the ribbon when the cassette is not mounted on the machine, having a portion which can be inserted into a slot in the casing.
German utility model No. 68 03 26 07.4 discloses a cassette of that type which has an anti-unrolling element in the form of a holding blade portion having a central groove. The blade portion is inserted into a seat in the casing and, by means of the central groove, is engaged and guided on a sleeve on which the tube of the supply spool is rotatable. The blade portion is inserted between the lower part of the cover and the upper edge of the ribbon until it is stopped with the bottom of the groove against the sleeve. The length of the blade portion is such that it engages all the turns of the ribbon which is wound on the supply spool, thus compressing the spool against the bottom of the casing. The blade portion prevents undesirable unrolling movements of the ribbon but it suffers from disadvantages. In particular, the blade portion engages the upper edge of the ribbon with the rather limited width of the blade portion, during insertion thereof, while it remains in the casing and during withdrawal thereof, whereby it causes substantial squashing with deformation of the upper edge of the ribbon.